The invention relates to a sewing machine controlled by a computer for producing a relative movement between a sweing head with a needle and at least one workpiece holder receiving a workpiece to be sewn during a sewing process in a plane substantially perpendicular to a direction of movement of the needle, whereby for producing said relative movement in two coordinate directions at right angles to one another servomotors controlled by said computer are provided for moving said sewing head relative to the at least one workpiece holder and whereby at the end of a sewing process the sewing head and the workpiece holder are brought into a position relative to one another in which the workpiece holder is free from the sewing head.
In such a sewing machine known from U.S. Pat. No. 4,503,789 two juxtaposed workpiece holders are adjacently arranged in one coordinate direction in a fixed work plate and can be alternately supplied, namely when the workpiece portions located in the other workpiece holder are to be sewn together. Such workpiece holders conventionally comprise a relatively thin lower plate and an upper plate pivotable with respect thereto in the manner of a cover and between which are clamped the workpiece portions to be sewn together following the closing of the workpiece holder. Recesses are provided in the upper and lower plates corresponding to the seam configuration to be produced. Particularly if the start and finish of the seam to be produced are relatively close together, then the plate section surrounded by the recess in the lower plate is relatively unstable, i.e. flexible. This more particularly applies in view of the fact that the lower plate is very thin, so that the material to be sewn which bridges the recess cannot be drawn out downwards. Particularly if relatively narrow parts are to be sewn together, there is a risk that they will not be adequately secured between the upper plate or its plate portion surrounded by the recess and the lower plate or its plate portion surrounded by its recess.
U.S. Pat. No. 3,839,973 discloses a sewing machine having two endless belts for the transfer of the workpiece. These two endless belts leave a narrow slit free between them in the vicinity of the stitch formation point. They are both synchronously driven in such a way that the workpiece is correspondingly guided over the stitch formation point. In order to keep the workpiece on said belts, it is subject to vacuum action from below through said belts.
U.S. Pat. No. 4,362,077 discloses a cutting mechanism where, above a cutting table, is provided a cutting head which can move in two coordinate directions. For pressing the cutting material flexible belts of ferromagnetic material are provided parallel to one another and accompanied by the clamping of the cutting material by means of fixed magnets in the cutting table are pressed against the same. The belts are formed into a loop in the cutting head and are guided over pulleys adjacent to the cutting point, so that the latter is always free.